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Proceedings of the Royal Society of Edinburgh. [Sess. 
were extracted twice with cold distilled water, and the filtered extract was 
mixed with phosphoric acid and distilled until the liquid in the retort 
became syrupy. The distillate so obtained had a slight but distinct acid 
reaction. Since it was considered that if formic acid were present in this 
distillate its presence should be readily established by converting it into 
lead formate and submitting this to examination under the polarising 
microscope, the distillate was mixed with excess of moist lead hydroxide 
which had been precipitated from a solution of lead nitrate, in presence of 
phenol phthalein, by the addition of sodium hydroxide until a rose colora- 
tion was just distinguishable, and had been subsequently washed with 
water eight times by decantation. After standing for a short time, the 
mixture was filtered, and the filtrate was saturated with carbon dioxide 
and then evaporated to dryness on the steam bath. The residue was 
extracted with a few drops of hot water, and the filtered extract was 
evaporated to dryness over sulphuric acid, portions of it having been 
placed upon a number of microscope slides with a view to obtaining any 
crystalline residue in a form suitable for optical examination. 
Several successive preparations were carried out, in the manner just 
described, with varying quantities of material from nettles, and a collection 
of slides was obtained. In some later experiments, preparations were 
made in which barium hydroxide was substituted for the lead hydroxide 
mentioned above, and additional slides were obtained carrying residues 
which should contain barium formate if formic acid were present in the 
acid distillates. A large number of slides of both descriptions were 
examined with great care by Mr David Balsillie, B.Sc., whose report upon 
them is included here : — 
“ The majority of the earlier slides, carrying lead salts derived from 
nettles, which were submitted for examination, exhibited only dendritic 
growths which were isotropic and of no value for determinative work. 
Several of the later preparations, however, were distinctly more satis- 
factory, and showed crystalline substance occurring as ( a ) stellate groupings 
of strongly bi-ref ringent needles, and ( b ) single crystals with well-developed 
faces and sharp edges. The characters of these, respectively, were briefly 
as follows: — 
“ (a) The needles invariably showed straight extinction, were of dis- 
tinctly higher refractive index than methylene iodide, and always had 
the faster ray vibrating along their length. Their general resemblance in 
these (as well as other) particulars to similar preparations of known lead 
formate was exceedingly striking. Plathan * asserts that lead formate 
* See Groth, Chemische Krystallograjohie, iii Teil (1910), p. 17. 
